Attenuation of seismic waves and the universal rheological model of the Earth’s mantle

Izv., Phys. Solid Earth

2015

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The laboratory tests of rock specimens show that transient creep, at which deformations increase with time whereas strain rate decreases occurs when creep strains are sufficiently small. Since plate tectonics only permits small deformations in the lithospheric plates, the creep of the lithosphere is transient (non steady state). In this work, we study how the rheology of the lithosphere that possesses elasticity, brittleness (pseudo plasticity), and creep affects the folding in the Earth's crust. Folding is caused by horizontal com pression that results from the collision between the lithospheric plates. The effective viscosity characterizing the transient creep is lower than in the case of a steady state creep and depends on the characteristic time of the considered process. The allowance for transient creep gives the distribution of the rheological properties of the horizontally compressed lithosphere in which the upper crust is brittle, whereas the lower crust and mantle lithosphere are dominated by transient creep. It is shown that the flows that arise in the lithosphere due to the instability under horizontal compression and cause folding are small scale. These flows are con centrated in the upper brittle crust, they determine the short wave Earth's surface topography, penetrate into the lower, creep dominated crust to a shallow depth, and do not penetrate into the mantle. Therefore, these flows do not deform the Moho.

Section: Transient Creep Of the Rocksmentioning

confidence: 98%

Rheology of the lithosphere and the folding caused by horizontal compression

Izv., Phys. Solid Earth

2015

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“…As mentioned above, the diffusion creep can be ignored when considering the processes in the upper mantle and lithosphere, where the contri bution of this rheological mechanism to deformation is negligible. The contribution of low temperature dis location creep, as shown in (Birger, 2007), should be considered only in the study of fast processes, such as attenuation of seismic waves.…”

Section: Nonlinear Integral Model Of Creepmentioning

confidence: 99%

“…If the strain rate is high, the memory depth is small, and even flows with rapidly changing velocities can be regarded as quasi station ary. For flows, causing minor strains and superim posed on a basic stationary or quasi steady flow, non linear rheological model (10) The universal rheological model constructed in (Birger, 2007) is a series connection of four rheological elements that describe high temperature dislocation creep, low temperature dislocation creep, diffusion creep and elasticity. As mentioned above, the diffusion creep can be ignored when considering the processes in the upper mantle and lithosphere, where the contri bution of this rheological mechanism to deformation is negligible.…”

Section: Nonlinear Integral Model Of Creepmentioning

confidence: 99%

Transient creep of the lithosphere and its role in geodynamics

Izv., Phys. Solid Earth

2012

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Laboratory experiments with samples of rocks show that at small strains there is transient creep, at which the strain grows with time, and the strain rate decreases. Plate tectonics allows only small strains in the lithospheric plates, so that the lithosphere creep is transient. In geodynamics, the lithosphere is regarded as a cold boundary layer formed by mantle convection. If we assume that the lithosphere has a steady state creep, which is described by power law non Newtonian rheological model, the low effective viscosity of the lower layers of the lithosphere, obtained by data on small scale postglacial flows, is possible only at high strain rates in these layers. However, the high strain rates in the lithosphere induce large strains that contradict plate tectonics. Transient creep of the lithosphere leads to its mobility at small strains, removing the discrepancy between thermal convection in the mantle and plate tectonics, which holds in the case of power law rheolog ical model of the lithosphere.

“…If the strain rate is high, the memory depth is small, and even flows with rapidly changing velocities can be regarded as quasi-stationary. For flows, causing small strains and superimposed on a basic stationary or quasi-steady flow, the non-linear rheological model (10) The universal rheological model constructed in Birger (2007) is a series connection of three rheological elements that describe hightemperature dislocation creep (here, the term 'high-temperature creep' means creep at a temperature sufficiently close to the melting point temperature), low-temperature dislocation creep described by the Lomnits rheology and diffusion creep. As mentioned earlier, the diffusion creep can be ignored in the upper mantle and lithosphere: the contribution of this rheological mechanism to deformation is negligible here.…”

Section: N O N -L I N E a R I N T E G R A L M O D E L O F C R E E Pmentioning

confidence: 99%

“…At low temperature, the Andrade parameter is large and the Lomnits stage is long. The contribution of low-temperature dislocation creep described by the Lomnits rheology should be considered only in the study of fast processes such as attenuation of seismic waves (Birger 2007). The Andrade rheology also applies in the study of the attenuation of seismic waves (Berckhemer et al 1979).…”

Section: N O N -L I N E a R I N T E G R A L M O D E L O F C R E E Pmentioning

confidence: 99%

Transient creep and convective instability of the lithosphere

Geophysical Journal International

2012

SUMMARY Laboratory experiments with rock samples show that transient creep, at which strain grows with time and strain rate decrease at constant stress, occurs while creep strains are sufficiently small. The transient creep at high temperatures is described by the Andrade rheological model. Since plate tectonics allows only small deformations in lithospheric plates, creep of the lithosphere plates is transient whereas steady‐state creep, described by non‐Newtonian power‐law rheological model, takes place in the underlying mantle. At the transient creep, the effective viscosity, found in the study of postglacial flows, differs significantly from the effective viscosity, which characterizes convective flow, since timescales of these flows are very different. Besides, the transient creep changes the elastic crust thickness estimated within the power‐law rheology of the lithosphere. Two problems of convective stability for the lithosphere with the Andrade rheology are solved. The solution of the first problem shows that the state, in which large‐scale convective flow in the mantle occurs under lithospheric plates, is unstable and must bifurcate into another more stable state at which the lithospheric plates become mobile and plunge into the mantle at subduction zones. If the lithosphere had the power‐law fluid rheology, the effective viscosity of the stagnant lithospheric plates would be extremely high and the state, in which large‐scale convection occurs under the stagnant plates, would be stable that contradicts plate tectonics. The mantle convection forms mobile lithospheric plates if the effective viscosity of the plate is not too much higher than the effective viscosity of the underlying mantle. The Andrade rheology lowers the plate effective viscosity corresponding to the power‐law fluid rheology and, thus, leads to instability of the state in which the plates are stagnant. The solution of the second stability problem shows that the state, in which the lithospheric plate moves as a whole with constant velocity, is stable but small‐amplitude oscillations are imposed on this motion in regions of thickened lithosphere beneath continental cratons (subcratonic roots) where the thickness of the lithosphere is about 200 km. These oscillations create small‐scale convective cells (the horizontal dimensions of the cells are of the order of the subcratonic lithosphere thickness). Direction of motion within the cells periodically changes (the period of oscillations is of the order of 108 yr). The small‐amplitude convective oscillations cause small strains and do not destroy the thickening of the lithosphere beneath cratons. Thus, the transient creep of the lithosphere explains not only mobility of the lithospheric plates but longevity of subcratonic roots as well.